Images get very blue, and very washed out. The light can be very harsh, ... . I am also shooting through 4 inches of "glass" and that acts like another filter.
Colour balance: At altitude, all is blue. I manage that in PS. But could I make better selections in camera.
Any advice would be gratefully received.
The sky from the ground is blue because of scattered light, blue being more easily scattered. Shadows are are lit by scattered light and appear blue or cool for that reason.
At high altitude, the sky above is blackish (even black if you go high enough), not blue. From an F4 at 65000 feet, the upper sky is black. Not much to scatter light from space back to your camera. The moon and other objects in the upper sky are lit by pure sunlight, and shouldn't look blue. Harsh, yes. Unless you are shooting near toward the horizon and through some extra air. It also depends on the direction relative to the sun you are shooting. Sunsets are red beause the blue is scattered out by the air. Shooting object toward the horizon and sun are redder.
There is a movie technique called "day for night." The images are made in the day, under exposed to look dark and shot with a blue (passes blue) filter. That is suppose to look OK because objects at night are illuminated by scattered blue light. Dim and blue.
The blue stuff should be associated with shooting down and images being illuminated with scattered light. A UV filter might help, but freuently they are "warmered" (added magenta) to reduce blue. Not just UV.
I have taken images using only UV light. There was a 10 stop filter factor and it was impossible to see thought the filter. The images were fine, but I concluded not much of the total exposure is from UV (10 stop filter factor). I think your problem is scattered blue light.
Have you checked your camera/lens/airplane window combo for sensitivity to UV? You may need a magenta warming filter instead of a UV.